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When you have acquired your evidence in the form of articles, books, and other resources, you need to evaluate and critique your sources. Evaluate information on its level of evidence and quality. Different criteria are used to determine the quality of evidence and information sources. The Evidence-Based Medicine Pyramid provides and overview on the types of evidence available and the quality of each. 

Critical Appraisal

Critically appraising and assessing source with an eye for:


Trials that are randomized and double blind, to avoid selection and observer bias, and where we know what happened to most of the subjects in the trial. Does the result help answer my question? Is the patient population similar enough to my patient?


Trials that mimic clinical practice, or could be used in clinical practice, and with outcomes that make sense. Valid results make for strong evidence. For instance, in chronic disorders we want long-term, not short-term trials. We are also interested in outcomes that are large, useful, and statistically very significant (p < 0.01, a 1 in 100 chance of being wrong).


Trials (or collections of trials) that have large numbers of patients, to avoid the random play of chance. A large treatment effect across a large population indicate important results. Are the results clinically, as well as statistically, significant?  For instance, to be sure that a number needed to treat (NNT) of 2.5 is really between 2 and 3, we need results from about 500 patients. If that NNT is above 5, we need data from thousands of patients.

Adapted from Critical Appraisal, Bandolier

Evaluating Sources

  • Accuracy - Are there errors? Is the information fact-based?
  • Currency- Has the information been updated recently? Does the information need to be current to be relevant?
  • Authority- What is the author's affiliation? What is the author's background and expertise?
  • Objectivity- Is there any bias? What is the purpose of the information being published?
  • Coverage- Is the content in-depth or an overview?

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